Presently, there is no known therapy that can target invading glioma tumor cells. In order to study the biological properties of invading glioma cells at the molecular level, we have developed an in vivo animal model using green fluorescent protein (GFP)-tagged murine GL261 glioma cells. This allows us to identify invading glioma cells into the brain adjacent to the main tumor mass using GFP immunohistochemistry. Microarray gene technology high-lighted differences in gene expression profiles between invading and non-invading human glioma cells identifying MHC class I molecules as a potential target for novel immunotherapeutic approaches. The GL261 glioma cell line is poorly immunogenic due to its low expression of MHC molecules. However, we have shown that low dose whole brain radiation therapy (WBRT) of an established GL261 tumor up-regulates MHC expression on invading GL261 glioma cells in vivo. In the present application we will continue to test the hypothesis that low dose WBRT to the GL261 intracranial tumor will up-regulate MHC expression providing a target(s) for a T-cell mediated antitumor immune response directed towards the invading cells and improve the efficacy of immunotherapy. In Aim 1 we will determine the optimal dose and time course to up-regulate MHC expression on invading glioma cells and optimal number of vaccinations to increase long-term survivals, respectively (1a); and to determine host's immune response elicited by the combination of WBRT and vaccination (V). The WBRT schedule of 4 Gy alone induces an inflammatory response associated with an influx of TILs at the tumor site. Brains will be characterized for TILs by FACS analysis and immunohistochemistry of frozen section at 1 week and 2 weeks following treatments. (1b). In Aim 2, we will determine the effects of MHC overexpression in GL261 tumor cells on their growth, invasion and immunogenicity in vitro and in vivo. GL261 tumor cells will be engineered to stably express an inducible construct (Tet-On) encoding the murine CIITA cDNA, a gene that regulates expression of the MHC complex. In Aim 3, we will determine whether up-regulation of MHC expression on invading GL261 tumor cells in vivo is required for the improved therapeutic effect of vaccination following WBRT. MHC expression will be inhibited using siRNA technology. The growing awareness that low dose irradiation can make tumors more amenable to recognition by the patients' immune system forms the basis of our rationale combining cancer vaccines with local irradiation of the brain tumor. [unreadable] [unreadable] [unreadable]